Bioavailability of Metals and Arsenic on Brownfield Land: Remediation or Natural Attenuation for Risk Minimization? - Environmental Contamination: Health Risks and Ecological Restoration - page 474

restoration.or.remedial.actions.may.be.entirely.driven.by.mitigation.of.risk.
which.itself.is.informed.by.a.misguided.interpretation.of.science.
Remedial. actions. have. moved. from. dig-and-dump. or. concealment,. to.
physicochemical. amelioration,. phytomanagement,. and. monitored. natural.
attenuation.(CL:AIRE.2008)..The.costs.of.these.more.modern.remedial.actions.
and.technologies.often.represent.only.a.small.fraction.of.site.engineering.costs.
and.can.be.justiied.on.the.basis.of.(1).the.restoration.of.land.and.property.
values. or. (2). the. establishment. of. safe. and. accessible. green. space. (reserves.
or.gardens).for.urban.dwellers..Restored.land.and.green.space.creates.a.safe.
and.healthy.environment,.providing.improved.biodiversity.and.provision.of.
ecosystem. services.. We. question. whether. these. frequently. deined. but. sel-
dom. quantiied. aspirational. outcomes. are. realistic.. Based. on. a. selection. of.
case.studies,.this.paper.considers.whether.elevated.trace.elements.do.present.
a.signiicant.risk.in.the.urban.environment.and.what.beneits.are.achieved.
following.concerted.site.restoration..We.focus,.in.particular,.on.one.recently.
completed.restoration.project.in.which.a.contaminated.canal.sediment.and.
adjacent.industrial.land.was.converted.to.an.urban.nature.reserve.

Bioavailability
Using.a.meta-analysis.of.12.agricultural.soils.contaminated.by.4.metals.for.
different. periods. of. time. up. to. 13. years,. Black. (2010). showed. that. consid-
erable. differences. existed. between. 6. different. estimates. of. bioavailability.
(Table.22.1)..All.of.the.data.referred.to.prediction.of.uptake.into.wheat.and.
ryegrass..While.Ca.(NO 3 ) 2 .provided.reliable.estimates.of.Zn.and.Ni.uptake,.
a.range.of.between.only.46%.and.84%.could.be.explained.by.this.extractant.

TABLE 22.1
Coeficients.of.Variation.( r 2 ).Ranges.for.Six.Measures.of.Metal.
Bioavailability a .versus.Uptake.into.Wheat.Seedling.or.Pasture.Ryegrass,.
and.the.Best.Predictors.of.Uptake.in.Each.Case

Cd Cu Ni Zn n

Wheat.seedlings 0.13-0.63 0.27-0.34 0.53-0.71 0.46-0.66 335-502

Best predictor EDTA Pseudo-total Ca(NO 3 ) 2 Ca(NO 3 ) 2

Pasture.ryegrass 0.37-0.70 0.21-0.45 0.51-0.84 0.46-0.68 236-325

Best predictor Rhizon Pseudo-total Ca(NO 3 ) 2 Ca(NO 3 ) 2

All.data.combined 0.20-0.49 0.27-0.34 0.56-0.72 0.49-0.64 538-754

Best predictor DGT Pseudo-total Ca(NO 3 ) 2 Ca(NO 3 ) 2
Data. are. from. studies. on. 12. soil. types. in. New. Zealand,. between. 6. months. and.
13.years.after.spiking.and.application.of.biosolids.(2.3%-9.8%C,.pH.5.1-6.1).
a. Pseudo-total.(HNO 3 -extractable),.EDTA,.Ca(NO 3 ) 2 ,.Rhizon.soil.moisture.samplers,.
DGT,.Free.ion.activity.(WHAM).